The Republican Party, traditionally an admirer of free enterprise, has discovered the virtues of government regulation, at least when it comes to its phone bill.

Michigan Bell has decided that a fair price for installing 10,000 phones for the GOP National Convention in Detroit in July is $400 -- per phone.

GOP leaders and representatives of the three major television networks, who rarely agree on anything, think that is too much, especially considering that the normal installation fee is $38.

So the GOP and the media representatives have taken the case to the Michigan Public Service Commission, which regulates the telephone company. The discovery phase of the hearing began today before an administrative law judge.

"Their estimates are based on what they call the 'Kansas City experience,'" said Detroit area attorney Thomas Boyer, representing the media. "We are not sure where they got their number for this experience."

Boyer said he did not know specifically the phone bill for the 1976 Republican convention in Kansas City, "but it was substantially less than what they are being charged here in Detroit."

One informed estimate was that installation at the 1976 convention was about $200 per phone.

The squabble began at the end of October, when Bell filed a request for the special rate with the commission. Bell spokesman Bill Hensley said the figure was reached "after thorough, exhaustive and a long, detailed analysis."

"You have to look at the magnitude of what we're talking about," hensley said. He pointed out that the convention will need about 6,700 telephone lines and 10,000 telephones.

"That is enough telecommunications to serve a medium-sized city," Hensley said. "We're being asked to build a telephone company within a telephone company in a very short period of time. It is probably the biggest service job Michigan Bell has ever undertaken."

Hensley said the company estimates the total cost for this mammoth undertaking at more than $3 million. And that is with no profit.

"The rates are designed to cover all the costs, so that none of the costs have to be borne by Michigan's 3 million consumers. That's a political contribution," he said.

Republican Party leaders and the media insist that they do not want to freeload off Michigan's taxpayers. But they still find the $400 installation charge a bit outlandish.

In addition to the installation fee, Bell is proposing a flat $48 monthly fee for each telephone. Since some phones will be installed as early as Jan. 18, some cutomers would be paying for telephones that sit unused for five months.

To ease the financial burden somewhat, Ma Bell is including a number of special convention features. For instance, every phone connected with the convention will have a special "467" telephone prefix, which corresponds to the letters "GOP on the dial.

Also, convention delegates housed as far away as Ann Arbor -- some 50 miles outside Detroit -- will have unlimited local calling, and the same "467" prefix.

A hearing has been scheduled next week. The three-member Michigan Public Service Commission has indicated it will expedite its decision.